The present invention relates to phthalazine derivatives, to the pharmaceutical compositions containing them and to their use as phosphodiesterase 4 inhibitors. Phosphodiesterases are a family of isoenzymes which constitute the basis of the main mechanism of cAMP (cyclic adenosine-3xe2x80x2,5xe2x80x2-monophosphate) hydrolytic inactivation. cAMP has been shown to be the second messenger mediating the biologic response to many hormones, neurotransmitters and drugs [Krebs Endocrinology Proceedings of the 4th International Congress Excerpta Medica, 17-29, 1973]. When the suitable agonist binds to the cell surface, the adenylated cyclase activates and turns Mg2+-ATP into cAMP. cAMP modulates the activity of the majority, if not of all the cells contributing to the pathophysiology of various respiratory diseases, both of allergic origin and not. It follows that an increase of the cAMP concentration yields beneficial effects such as airway smooth muscle relaxation, inhibition of the mast cell mediator release (basophil granulose cells), suppression of the neutrophil and basophil degranulation, inhibition of the monocyte and macrophage activation. Thus, compounds able of activating adenylate cyclase or of inhibiting phosphodiesterases could suppress the undesired activation of the airway smooth muscle and of a great number of inflammatory cells.
In the phosphodiesterase family there is a distinct group of isoenzymes, phosphodiesterases 4 (hereinafter PDE 4) specific for the cAMP hydrolysis in the airway smooth muscle and inflammatory cells (Torphy, xe2x80x9cPhosphodiesterase Isoenzymes: Potential Targets for Novel Anti-asthmatic Agentsxe2x80x9d in New Drugs for Asthma, Barnes, ed. IBC Technical Services Ltd, 1989). Studies carried out on this enzyme show that its inhibition yields not only the airway smooth muscle relaxation, but also the suppression of mastocyte, basophil and neutrophil degranulation, so as the inhibition of the monocyte and neutrophil activation. Thus PDE 4 inhibitors are effective in the therapy of asthma. Such compounds offer a unique approach to the therapy of various respiratory diseases, both of allergic origin and not, and possess significant therapeutic advantages over the current therapy.
The excessive or irregular production of tumour necrosis factor (hereinafter TNFxcex1) a cytokine with pro-inflammatory activity produced by various kinds of cells, affects the mediation or the exacerbation of many pathologies such as, for example, the adult respiratory distress syndrome (ARDS) and the chronic pulmonary inflammatory disease. Therefore compounds able to control the negative effects of TNFxcex1, i.e. the inhibitors of this cytokine, are to be considered as useful against many pathologies. The patent application EP-0 017 411 (in the name of Pfizer) illustrates phthalazines of formula: 
wherein
R1 is a lower alkyl; and Y is xe2x80x94(CH2)mxe2x80x94Z wherein m is 1 or 2 and Z is carbamoyloxy, carbonylamino, sulphamoyl, ureido, amino-sulphamoyl, carboxyamino substituted in the terminal position by a (C3-7)cycloalkyl. These compounds are said to be inhibitors of the phosphodiesterases with stimulant function on the cardiac muscle, therefore their activity does not relate to PDE 4.
The patent application EP-0 722 936 (in the name of Eisai) claims, inter alia, compounds of formula: 
wherein n=0-4; R1 is optionally substituted lower alkoxy, optionally substituted cycloalkyl, or a xe2x80x94OR9 group wherein R9 represents an optionally substituted arylalkyl group; X is xe2x80x94Nxe2x95x90 or xe2x80x94NR6xe2x80x94 wherein R6 is hydrogen, a lower alkyl group, or optionally substituted arylalkyl or heteroarylalkyl groups; Y is xe2x80x94CO or xe2x80x94CBxe2x95x90 wherein B is xe2x80x94NR7R8 wherein one of R7 and R8 may be H and the other an optionally substituted heteroarylalkyl group, or B is hydrogen or an optionally substituted aryl, heteroaryl, arylalkyl or heteroarylalkyl group; A is a hydrogen or halogen atom, or an optionally mono or disubstituted amino group, an optionally substituted aryl, heteroaryl or heteroarylalkyl group. Among the groups optionally substituting the above mentioned residues halogen atoms are cited. These compounds are said to be active as inhibitors of cGMP-PDE, i.e. PDE 5, a phosphodiesterase just acting through a cGMP-dependent mechanism and whose field of application is markedly cardiovascular (Schudt C. et al., Phosphodiesterase Inhibitors, Academic Press). The patent U.S. Pat. No. 3,274,185 (in the name of Messengill) describes, inter alia, phthalazines of formula: 
wherein Y and Y1 are lower alkoxy; Z is phenyl optionally substituted by halogen or benzyl; and R is hydrogen. These phthalazines are endowed with sedative and hypotensive activity, with no mention of the mechanism of action.
The patent U.S. Pat. No. 3,813,384 (in the name of Asta-Werke) illustrates, inter alia, benzylphthalazinones of formula: 
wherein R1 and R2 are lower alkoxy or halogen; X is 5 an optionally branched alkylene chain; m and n are 1-3; p is 0 or 1; and 
the group is a C3-8 mono-, di- or tricyclic residue containing one or two nitrogen atom(s). Such compounds have hystaminolytic action and are useful, for example, in the treatment of asthma.
The patent application NL 8005411 (in the name of Mitsubishi Yuka) describes phthalazines of formula: 
wherein X is oxygen or NH; R1, R2 and R3 are, inter alia, (C1-5)alkyl, (C1-5)alkoxy, halogen or CF3, n, m and p are 0-3. These compounds are used as inhibitors of the piastrinic aggregation.
The patent application JP-56061365 (in the name of Showa Denko) describes phthalazinones of formula: 
wherein, inter alia, R is halogen and n is 1-3, as vasodilators and anti-ulcer.
It has now been surprisingly found a new class of phthalazine derivatives able to inhibit PDE 4 and TNFxcex1.
Therefore the present invention relates to compounds of formula I 
wherein
 is a single or double bond;
B is NH, methylene, a C2-6 alkylene chain optionally branched and/or unsaturated and/or interrupted by a C5-7 cycloalkyl residue;
A is phenyl or heterocycle optionally substituted by one or more substituent(s) or a COR4 group wherein R4 is hydroxy, C1-4alkyl, amino optionally mono- or di-substituted by a C1-6-alkyl group or monohydroxylated;
R represents two hydrogen atoms or a Cxe2x95x90O group when  is a single bond or, when  is a double bond, is hydrogen, optionally substituted aryl or heterocycle, (C1-8)-alkyl, (C2-8)-alkenyl or (C2-8)-alkynyl optionally substituted by aryl or heterocycle; aryloxy, heterocyclyloxy, aryl-C1-4-alkoxy, heterocyclyl-C1-4-alkoxy, amino substituted by one or two C1-4-alkyl group(s), aryl-amino, heterocyclyl-amino, aryl-C1-4-alkyl-amino, heterocyclyl-C1-4-alkylamino;
R1 is a C1-6-alkyl, aryl, aryl-C1-10-alkyl, C4-7-cycloalkyl group optionally containing an oxygen atom and/or substituted by a polar substituent;
R2 is a C1-6-alkyl, polyfluoroC1-6-alkyl group;
R3 is absent when  is a double bond, or, when  is a single bond, is hydrogen;
C1-6-alkyl optionally substituted by aryl, by heterocycle or by a COR5 group wherein R5 is hydroxy, C1-4-alkoxy or hydroxyamino;
xe2x80x94COR6 wherein R6 is hydrogen, aryl, aryl-C1-6-alkyl, amino optionally alkylated or monohydroxylated, hydroxy, C1-4-alkoxy, carboxy, C1-4-alkoxycarbonyl, 
xe2x80x83or C1-4-alkyl optionally substituted by heterocycle;
d) C1-4-alkyl-sulfonyl;
the Nxe2x86x92O derivatives of the compounds of formula I and the pharmaceutically acceptable salts thereof;
provided that when  is a double bond, A is phenyl or nitrogen heterocycle, and R1 is an aryl, aryl-C1-10-alkyl, C4-7-cycloalkyl optionally containing an oxygen atom and/or substituted by a polar substituent; then R is different from hydrogen, phenyl or (C1-4)alkyl optionally substituted by aryl.
The proviso present in the meanings of formula I has the aim of excluding the compounds described in the Italian patent application no. MI97A002806 in the name of the same Applicant.
Preferred compounds of formula I are those wherein  is a single or double bond;
B is methylene or a C2-6 alkylene chain; A is phenyl or heterocycle optionally substituted by one or more substituents; R represents two hydrogen atoms or a group xe2x95x90O when  is a single bond, or, when  is a double bond, is hydrogen, optionally substituted aryl or heterocycle, (C1-8)-alkyl, (C2-8)-alkenyl or (C2-8)-alkynyl optionally substituted by aryl or heterocycle; aryloxy, heterocyclyloxy, aryl-C1-4-alkoxy, heterocyclyl-C1-4-alkoxy, amino substituted by one or two C1-4-alkyl, aryl-amino, heterocyclyl-amino, aryl-C1-4-alkyl-amino, heterocyclyl-C1-4-alkylamino groups; R1 is a C1-6-alkyl, aryl, aryl-C1-10-alkyl, C4-7-cycloalkyl group optionally containing an oxygen atom and/or substituted by a polar substituent; R2 is a C1-6-alkyl, polyfluoroC1-6-alkyl group; R3 is absent when  is a double bond, or, when  is a single bond, is hydrogen;
C1-6-alkyl optionally substituted by aryl, by heterocycle or by a COR5 group wherein R5 is hydroxy, C1-4-alkoxy or hydroxyamino;
xe2x80x94COR6 wherein R6 is hydrogen, aryl, aryl-C1-6-alkyl, optionally alkylated or monohydroxylated amino, hydroxy, C1-4alkoxy, carboxy, C1-4-alkoxycarbonyl, or C1-4-alkyl optionally substituted by heterocycle;
C1-4-alkyl-sulfonyl;
the Nxe2x86x92O derivatives of the compounds of formula I and the pharmaceutically acceptable salts thereof;
provided that when  is a double bond, A is phenyl or nitrogen heterocycle, and R1 is an aryl, aryl-C1-10-alkyl, C4-7-cycloalkyl group optionally containing an oxygen atom and/or substituted by a polar substituent; then R is different from hydrogen, phenyl or (C1-4)alkyl optionally substituted by aryl.
Still more preferred compounds of formula I are those wherein  is a double bond;
B is methylene; A is pyridine substituted by one or more substituents; R is optionally substituted aryl or heterocycle, (C1-8)-alkyl, (C2-8)-alkenyl or (C2-8)-alkynyl optionally substituted by aryl or heterocycle, aryloxy, heterocyclyloxy, aryl-C1-4-alkoxy, heterocyclyl-C1-4-alkoxy, amino substituted by one or two C1-4-alkyl, aryl-amino, heterocyclyl-amino, aryl-C1-4-alkyl-amino, heterocyclyl-C1-4-alkylamino groups; R1 is a C1-6-alkyl or C4-7-cycloalkyl group optionally containing an oxygen atom and/or substituted by a polar substituent; R2 is a C1-6-alkyl, polyfluoroC1-alkyl group; R3 is absent; the Nxe2x86x92O derivatives of the compounds of formula I and the pharmaceutically acceptable salts thereof.
The compounds of formula I may have one or more asymmetric centre(s) and thus be in the form of stereoisomers. Object of the present invention are compounds of formula I in the form of stereoisomeric mixtures so as of single stereoisomers.
The compounds of formula I are active as PDE 4 and TNFxcex1 inhibitors and thus are used as therapeutic agents in allergic and inflammatory pathologies such as, for example, emphysema, chronic bronchitis, asthma and allergic rhinitis.
As heterocycle pyrrole, imidazole, pyrazole, pyridine, pyrazine, pyrimidine, pyridazine, piperazine, triazine, morpholine, pyrrolidine, pyrroline, imidazoline, pyrazoline, pyrazolidine, imidazolidine, piperidine, fuiran, pyran, isothiazole, isoxazole, thiophene and the like are particularly meant. The substituents optionally present on A residues may be halogen, which means a fluorine, chlorine, bromine or iodine atom, oxo, nitro, carboxy, trifluoromethyl, amino.
Specific example of alkyl groups are methyl, ethyl, n-propyl, i-propyl, n-butyl, s-butyl, t-butyl, 2-methyl-propyl, n-pentyl, 1-methyl-butyl, 2-methyl-butyl, 3-methyl-butyl, 3-methyl-2-butyl, n-hexyl and the like. As (C5-7)cycloalkyl group cyclopentyl, cyclohexyl and cycloheptyl are meant, and when it is substituted by an oxygen atom, tetrahydrofuran or tetrahydropyran, for example, are meant, while aryl and aryl-C1-10-alkyl mean an aromatic ring or a system of 6-10 carbon atoms such as, for example, phenyl, benzyl, phenethyl, phenyl-pentyl, naphthyl, indanyl, indanyl-pentyl and the like.
The oxidised form Nxe2x86x92O, if present, may involve both the nitrogen atoms of the phthalazine ring and those present on A when it is a heterocyclic substituent.
Pharmaceutically acceptable salts of the compounds of formula I are those with organic and inorganic acids, such as, for example, hydrochloric, hydrobromic, hydroiodic, nitric, sulfuric, phosphoric, acetic, benzoic, maleic, fumaric, tartaric, citric, aspartic, succinic, methanesulfonic, 3,7-di-t.butylnaphthalen-1,5-disulfonic (dibudinic acid) or with inorganic bases such as, for example, sodium or potassium hydroxide, sodium bicarbonate.
The synthesis of the compounds of formula I proceeds according to methods known to the skilled in the art. For example, an acid of formula II; 
wherein R1 and R2 are as defined above, which, for example by treatment with a halogenating agent, for example thionyl chloride, is transformed into the corresponding acyl halide of formula III: 
wherein R1 and R2 are as defined above and X is chlorine or bromine. This compound is reacted with diethylamine in at least equimolar amounts, to give a benzamide of formula IV: 
wherein R1 and R2 are as defined above, which, with dimethylformamide in the presence of a strong organic base such as, for example, butyl-lithium, t-butyl-lithium, sec-butyl-lithium, and, optionally, of a ligand such as, for example tetramethylethylendiamine, gives a compound of formula Va: 
wherein R1 and R2 are as defined above, and RI is hydrogen.
When a compound of formula I wherein R is hydrogen is desired, the compound Va is reacted with an equimolar amount of ter-butylcarbazate to give the compound of formula VIa: 
wherein RI, R1 and R2 are as defined above, and Rxe2x80x2 is a protecting group of the carboxylic function such as, for example, t-butyl.
When a compound of formula I wherein R is different from hydrogen and  is a double bond is desired, the compound IV is treated with RII-magnesium halide, for example chloride, or RII-lithium, wherein RII is aryl, arylalkyl, arylalkenyl, arylalkynyl, heterocycle, heterocyclylalkyl, heterocyclylalkenyl, heterocyclylalkynyl, C1-8-alkyl, C2-8-alkenyl or C2-8-alkynyl, linear or branched, optionally interrupted by an heteroatom selected among oxygen and nitrogen and optionally substituted by a suitably protected hydroxy or oxo group, to give a compound of formula VII: 
wherein RII, R1 and R2 are as defined above. The compound VII is treated with a suitable oxidising agent such as, for example, pyridinium-chloro-chromate, and gives a compound of formula Vb: 
wherein R1, R2 and RII are as defined above, which treated with an equimolar amount of ter-butylcarbazate gives the compound of formula VIb: 
wherein R1, R2, Rxe2x80x2 and RII are as defined above.
The compound VIa or VIb is reacted with trifluoroacetic acid to give the phthalazinone of formula VIII: 
wherein R, R1 and R2 are as defined above. This phthalazinone is reacted with a halogenating agent such as, for example, phosphoryl chloride, to give the phthalazine of formula IX: 
wherein R, R1 and R2 are as defined above, and Xxe2x80x2 is a halogen atom.
Alternatively, the compound of formula VIII can be obtained directly from the compound of formula Va or Vb by treatment with hydrazine in acetic acid.
The compound IX gives a compound I by reaction with a compound of formula X
Axe2x80x94Bxe2x80x2xe2x80x94Yxe2x80x83xe2x80x83(X)
wherein A is as defined above, Bxe2x80x2 is methylene, ethylene or amino and Y is a metal such as, for example, Li, Na, Mg or a transition metal complex, gives a compound I wherein R has the above reported meanings when  is a double bond.
Alternatively, the compounds I wherein B is different from amino can be obtained starting from the acid of formula 11, which by reaction with formaldehyde/HCl gives a compound of formula XI: 
wherein R1 and R2 are as defined above. This compound is oxidised, for example with benzoyl peroxide/N-bromo-succinimide, and then hydrolysed to give a compound of formula XII: 
wherein R1 and R2 are as defined above, which with a halogenidric acid and triphenylphosphine gives a compound of formula XIII: 
wherein R1 and R2 are as defined above, which treated with an aldehyde of formula XIV:
Axe2x80x94Bxe2x80x3xe2x80x94CHOxe2x80x83xe2x80x83(XIV)
wherein A is as defined above and Bxe2x80x3 is methylene or a C2-5 alkylene chain optionally branched and/or unsaturated and/or interrupted by a C5-7 cycloalkyl residue, or is absent, in the presence of an organic base such as, for example triethylamine, gives a compound of formula XV: 
wherein R1, R2, Bxe2x80x3 and A are as defined above. This is reacted with hydrazine to give a compound of formula XVI: 
wherein R1, R2, and A are as defined above and B is different from amino, which is treated with a halogenating agent, such as phosphoryl chloride or bromide, to give a compound of formula XVII: 
wherein R1, R2, X and A are as defined above and B is different from amino. This compound subdue to a coupling reaction with the suitable metallo-organic derivative in the presence of a catalyst, for example, a palladium catalyst, or to a nucleophilic substitution gives a compound of formula I wherein  is a double bond and B is different from amino.
The compound of formula XVI reacted with a suitable alkyl halide or sulphonate in the presence of a base, for example, sodium hydride, gives a compound of formula I wherein R3 is a substituent different from hydrogen and R is xe2x95x90O.
Alternatively, the compound of formula XVII can be hydrogenated, for example with Pd/C in the presence of a base, to a compound of formula XVIII: 
wherein R1, R2, and A are as defined above and B is different from amino, which by further hydrogenation, for example with PtO2, gives the compound of formula XIX: 
wherein R1, R2, B and A are as defined above, which by subsequent treatment with the suitable acylating or sulphonating agent, gives a compound of formula I wherein  is a single bond and R3 is different from hydrogen.
The synthesis of the N-oxides of the compounds of formula I occurs by treating the compounds of formula I with peracids such as, for example, m-chloroperbenzoic acid.
The preparation of the salts of the compounds I is effected according to conventional methods.
The compounds of formula I are PDE 4 inhibitors as showed by the in vitro enzymatic inhibition activity tests (example 41), and also are able to inhibit the TNFxcex1 release. Comparisons with the following compounds were made: 6,7-dimethoxy-4-(pyridin-4-yl-methyl)-2H-phthalazin-1-one (reference 1) and 6,7-dimethoxy-4-(piperidin-4-yl-methyl)-2H-phthalazin-1-one (reference 2) comprised by the general formula of the patent application EP-0 722 936 (in the name of Eisai) already cited above, selected in view of their structural affinity with the compounds of the invention. The reference compounds, though chemically similar, showed to be inactive as PDE 4 inhibitors.
It is apparent how these selectivity and specificity features combined with the lack of activity on the cardiovascular system make the compounds of formula I specifically suitable for treating pathologies involving PDE 4 and TNFxcex1 such as asthma, the chronic obstructive pulmonary disease (COPD), the adult respiratory distress syndrome (ARDS), allergic rhinoconjunctivitis, psoriasis, atopic dermatitis, rheumatoid arthritis, septic shock, ulcerative cholitis, even if in the present contest the interest is particularly focused on the respiratory pathologies. Especially, the compounds of the invention are useful in the treatment of allergic and inflammatory diseases and above all in the therapy of COPD, asthma and allergic rhinitis.
The therapeutic doses shall be generally comprised between 0.1 and 1,000 mg a day and between 1 and 100 mg by oral route for single administration.
A further object of the present invention are the pharmaceutical compositions containing a therapeutically effective amount of the compounds of formula I or pharmaceutically acceptable salts thereof in admixture with a suitable carrier.
The pharmaceutical compositions object of the invention can be liquid, suitable for the enteral or parenteral administration, and, preferably, solid such as tablets, capsules, granulates, suitable for the oral administration, or in a form suitable for the transdermal and inhalatory administration.
The preparation of the pharmaceutical compositions object of the invention can be effected according to common techniques.